Control of dynamic lenses

ABSTRACT

Optical apparatus includes an electrically-tunable lens, including an electro-optical layer, having, for a given polarization of light incident on the layer, an effective local index of refraction at any given location within an active area of the electro-optical layer that is determined by a voltage waveform applied across the electro-optical layer at the location. Conductive electrodes extend over opposing first and second sides of the electro-optical layer and include an array of excitation electrodes. Control circuitry applies control voltage waveforms to the excitation electrodes. A polarization rotator is positioned and configured to intercept incoming light that is directed toward the lens and to rotate a polarization of the intercepted light so as to ensure that the light incident on the electro-optical layer has a component of the given polarization regardless of an initial linear polarization of the intercepted light.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/566,910, filed Sep. 11, 2019, which is a division of U.S. patentapplication Ser. No. 15/310,798, filed Nov. 14, 2016 (now U.S. Pat. No.10,466,391), in the national phase of PCT Patent ApplicationPCT/IB2015/053335, filed May 7, 2015, which claims the benefit of U.S.Provisional Patent Application 62/007,948, filed Jun. 5, 2014, and ofU.S. Provisional Patent Application 62/010,475, filed Jun. 11, 2014.Both of these provisional applications are incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates generally to optical devices, andparticularly to electrically-tunable lenses.

BACKGROUND

Tunable lenses are optical elements whose optical characteristics, suchas the focal length and/or the location of the optical axis, can beadjusted during use, typically under electronic control. Such lenses maybe used in a wide variety of applications. For example, U.S. Pat. No.7,475,985 describes the use of an electro-active lens for the purpose ofvision correction.

Electrically-tunable lenses typically contain a thin layer of a suitableelectro-optical material, i.e., a material whose local effective indexof refraction changes as a function of the voltage applied across thematerial. An electrode or array of electrodes is used to apply thedesired voltages in order to locally adjust the refractive index to thedesired value. Liquid crystals are the electro-optical material that ismost commonly used for this purpose (wherein the applied voltage rotatesthe molecules, which changes the axis of birefringence and thus changesthe effective refractive index), but other materials, such as polymergels, with similar electro-optical properties can alternatively be usedfor this purpose.

Some tunable lens designs use an electrode array to define a grid ofpixels in the liquid crystal, similar to the sort of pixel grid used inliquid-crystal displays. The refractive indices of the individual pixelsmay be electrically controlled to give a desired phase modulationprofile. (The term “phase modulation profile” is used in the presentdescription and in the claims to mean the distribution of the localphase shifts that are applied to light passing through the layer as theresult of the locally-variable effective refractive index over the areaof the electro-optical layer of the tunable lens.) Lenses using gridarrays of this sort are described, for example, in the above-mentionedU.S. Pat. No. 7,475,985.

PCT International Publication WO 2014/049577, whose disclosure isincorporated herein by reference, describes an optical device comprisingan electro-optical layer, having an effective local index of refractionat any given location within an active area of the electro-optical layerthat is determined by a voltage waveform applied across theelectro-optical layer at the location. An array of excitationelectrodes, including parallel conductive stripes extending over theactive area, is disposed over one or both sides of the electro-opticallayer. Control circuitry applies respective control voltage waveforms tothe excitation electrodes and is configured to concurrently modify therespective control voltage waveforms applied to excitation electrodes soas to generate a specified phase modulation profile in theelectro-optical layer.

U.S. Patent Application Publication 2012/0133891 describes anelectro-optical apparatus and method for correcting myopia that includesat least one adaptive lens, a power source, and an eye tracker. The eyetracker includes an image sensor and a processor operatively connectedto the adaptive lens and the image sensor. The processor is configuredto receive electrical signals from the image sensor and to control thecorrection power of the adaptive lens to correct myopia, with thecorrection power dependent on a user's gaze distance and myopiaprescription strength.

SUMMARY

Embodiments of the present invention that are described hereinbelowprovide improved electronically-tunable optical devices.

There is therefore provided, in accordance with an embodiment of theinvention, an optical device, which includes an electro-optical layer,having an effective local index of refraction at any given locationwithin an active area of the electro-optical layer that is determined bya voltage waveform applied across the electro-optical layer at thelocation. Conductive electrodes extend over opposing first and secondsides of the electro-optical layer. The electrodes include an array ofexcitation electrodes, which include parallel conductive stripesextending along respective, mutually-parallel axes across the first sideof the electro-optical layer. Each stripe is divided into two or moresegments extending over respective, mutually disjoint parts of an axisof the stripe. Control circuitry is coupled to apply respective controlvoltage waveforms to the segments of the excitation electrodes so as togenerate a specified phase modulation profile in the electro-opticallayer and is configured to concurrently modify the respective controlvoltage waveforms applied to one or more of the segments of each of aplurality of the excitation electrodes, thereby modifying a phasemodulation profile of the electro-optical layer.

Typically, the control circuitry is configured to apply the controlvoltage waveforms to the excitation electrodes so that the devicefunctions as a lens, having focal properties determined by the phasemodulation profile. In some embodiments, the control circuitry isconfigured to apply different, respective control voltage waveforms todifferent segments of at least some of the excitation electrodes, sothat the lens functions as a multifocal lens. In a disclosed embodiment,the two or more segments of each stripe include at least respectivefirst and second segments, such that the first segments of the stripestogether extend across a first area of the electro-optical layer, whilethe second segments of the stripes together extend across a second areaof the electro-optical layer. The control circuitry is configured toapply the different, respective control voltage waveforms so that thefirst area has a first focal length, and the second area has a secondfocal length, different from the first focal length.

In other embodiments, the device includes, for each stripe, one or moreswitches interconnecting the segments of the stripe and operable by thecontrol circuitry to electrically join or separate the segments of thestripe. Typically, the two or more segments of each stripe include atleast respective first and second segments, and the one or more switchesinclude a switch in each of the stripes interconnecting the respectivefirst and second segments, and the device includes a single control lineconnected to actuate the switch in each of the stripes so as toelectrically join or separate the first and second segments in all ofthe stripes simultaneously.

Additionally or alternatively, the two or more segments of each stripeinclude three or more segments connected in series by multiple switches,and the device includes multiple control lines connected to actuate themultiple switches across all of the stripes. In one embodiment, thecontrol circuitry is connected to at least one respective end of each ofthe conductive stripes and is configured to apply different, respectivecontrol voltage waveforms to different segments of at least some of theexcitation electrodes by, in alternation, actuating the multipleswitches and modifying the control voltage waveforms applied torespective ends of the conductive stripes.

There is also provided, in accordance with an embodiment of theinvention, optical apparatus, which includes an electrically-tunablelens. The lens includes an electro-optical layer, having, for a givenpolarization of light incident on the layer, an effective local index ofrefraction at any given location within an active area of theelectro-optical layer that is determined by a voltage waveform appliedacross the electro-optical layer at the location. Conductive electrodesextend over opposing first and second sides of the electro-opticallayer, the electrodes including an array of excitation electrodesextending across the first side of the electro-optical layer. Controlcircuitry is coupled to apply respective control voltage waveforms tothe excitation electrodes so as to generate a specified phase modulationprofile in the electro-optical layer. A polarization rotator ispositioned and configured to intercept incoming light that is directedtoward the lens and to rotate a polarization of the intercepted light soas to ensure that the light incident on the electro-optical layer has acomponent of the given polarization regardless of an initial linearpolarization of the intercepted light.

In disclosed embodiments, the polarization rotator includes aquarter-wave plate or a birefringent plate.

In some embodiments, the device includes a polarizer, which isinterposed between the polarization rotator and the electrically-tunablelens and is oriented so as to pass the component of the givenpolarization.

There is additionally provided, in accordance with an embodiment of theinvention, adaptive spectacles, which include a spectacle frame andfirst and second electrically-tunable lenses, mounted in the spectacleframe. Control circuitry is configured to receive an input indicative ofa distance from an eye of a person wearing the spectacles to an objectviewed by the person, and to tune the first and second lenses to havedifferent, respective first and second focal powers that bracket thedistance indicated by the input.

In some embodiments, the first and second lenses are mounted in thespectacle frame so as to apply the first and second focal powersrespectively to the light that is incident on the left and right eyes ofthe person.

Additionally or alternatively, the first lens is configured to apply thefirst focal power only to light of a first polarization, while thesecond lens is configured to apply the second focal power only to lightof a second polarization, orthogonal to the first polarization. In someembodiments, the first and second lenses are mounted in the spectacleframe so as to apply the first and second focal powers to the light thatis incident on a single eye of the person. In a disclosed embodiment,the spectacles include a polarization rotator, positioned and configuredto intercept incoming light that is directed toward the first and secondlenses and to rotate a polarization of the intercepted light so as toensure that the light incident on the first and second lenses hasrespective components of both of the first and second polarizationsregardless of an initial polarization of the incoming light.

In some embodiments, the spectacles include a sensor, configured tosense the distance from the eye of a person wearing the spectacles tothe object viewed by the person and coupled to provide the inputindicative of the distance to the control circuitry. Typically, thesensor is selected from a group of sensors consisting of an eye tracker,a camera configured to capture an image of the object, a rangefinder, aproximity sensor, and a trigger sensor operable by the person wearingthe spectacles.

Additionally or alternatively, the sensor is configured to sense a gazedirection of the eye toward the object, and wherein the controlcircuitry is configured to shift respective optical axes of the firstand second lenses responsively to the sensed gaze direction. The controlcircuitry may be configured to shift the optical axes in response to achange in the sensed gaze direction with a predefined time lag relativeto the change.

There is further provided, in accordance with an embodiment of theinvention, a method for producing an optical device. The method includesproviding an electro-optical layer, having an effective local index ofrefraction at any given location within an active area of theelectro-optical layer that is determined by a voltage waveform appliedacross the electro-optical layer at the location. Conductive electrodesare positioned so as to extend over opposing first and second sides ofthe electro-optical layer. The electrodes include an array of excitationelectrodes, which include parallel conductive stripes extending alongrespective, mutually-parallel axes across the first side of theelectro-optical layer. Each stripe is divided into two or more segmentsextending over respective, mutually disjoint parts of an axis of thestripe. Control circuitry is coupled to apply respective control voltagewaveforms to the segments of the excitation electrodes so as to generatea specified phase modulation profile in the electro-optical layer and toconcurrently modify the respective control voltage waveforms applied toone or more of the segments of each of a plurality of the excitationelectrodes, thereby modifying a phase modulation profile of theelectro-optical layer.

There is moreover provided, in accordance with an embodiment of theinvention, a method for producing optical apparatus. The method includesproviding an electrically-tunable lens, which includes anelectro-optical layer, having, for a given polarization of lightincident on the layer, an effective local index of refraction at anygiven location within an active area of the electro-optical layer thatis determined by a voltage waveform applied across the electro-opticallayer at the location. Conductive electrodes extends over opposing firstand second sides of the electro-optical layer. The electrodes include anarray of excitation electrodes extending across the first side of theelectro-optical layer. Control circuitry is coupled to apply respectivecontrol voltage waveforms to the excitation electrodes so as to generatea specified phase modulation profile in the electro-optical layer. Apolarization rotator is positioned to intercept incoming light that isdirected toward the lens and to rotate a polarization of the interceptedlight so as to ensure that the light incident on the electro-opticallayer has a component of the given polarization regardless of an initiallinear polarization of the intercepted light.

There is furthermore provided, in accordance with an embodiment of theinvention, a method for operating adaptive spectacles. The methodincludes mounting first and second electrically-tunable lenses in aspectacle frame. An input is received, indicative of a distance from aneye of a person wearing the spectacles to an object viewed by theperson. The first and second lenses are tuned to have different,respective first and second focal powers that bracket the distanceindicated by the input.

There is also provided, in accordance with an embodiment of theinvention, adaptive spectacles, which include a spectacle frame andfirst and second electrically-tunable lenses, mounted in the spectacleframe. A sensor is configured to output a signal indicative of a gestureperformed by an eye of a person wearing the spectacles. Controlcircuitry is configured to tune an optical characteristic of at leastone of the first and second lenses in response to the signal.

Typically, the gesture performed by the eye is selected from a group ofgestures consisting of eye movements, blinks and winks.

There is additionally provided, in accordance with an embodiment of theinvention, a method for operating adaptive spectacles. The methodincludes mounting first and second electrically-tunable lenses in aspectacle frame. A signal is received, indicative of a gesture performedby an eye of a person wearing the spectacles. An optical characteristicof at least one of the first and second lenses is tuned in response tothe signal.

The present invention will be more fully understood from the followingdetailed description of the embodiments thereof, taken together with thedrawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic, pictorial illustration of adaptive spectacles, inaccordance with an embodiment of the invention;

FIG. 2 is a schematic side view of an electronically-tunable lenssystem, in accordance with an embodiment of the invention;

FIG. 3A is a schematic, pictorial illustration of anelectronically-tunable lens, in accordance with another embodiment ofthe present invention;

FIGS. 3B and 3C are schematic frontal views of electrodes formed onopposing sides of the lens of FIG. 3A, in accordance with an embodimentof the present invention;

FIG. 3D is a schematic frontal of the lens of FIG. 3A, showing asuperposition of the electrodes on the opposing sides of the lens, inaccordance with an embodiment of the present invention;

FIG. 4 is a schematic frontal view of electrodes formed on anelectronically-tunable lens, in accordance with another embodiment ofthe invention; and

FIG. 5 is a schematic electrical diagram showing electrodes andswitching elements formed on an electronically-tunable lens, inaccordance with an alternative embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS Overview

Bifocal and multifocal lenses contain zones of different optical powers,in order to enable the person using the lens to see objects at differentdistances. This sort of multifocal capability enhances the ability ofthe lenses to correct the vision of people with limited capability fordistance accommodation (such as older people who suffer frompresbyopia). The zone structure of the lenses, however, limits the fieldof view at any given distance to the area of the zone of the lens thatprovides the required optical power for that distance.

Electrically-tunable spectacle lenses can provide a more flexible andcomfortable solution in such cases. The lenses may be coupled withsensors of various types in order to adjust the focal lengths andoptical axes of the lenses according to the object being viewed by theperson wearing the spectacles. Ideally, this sort of adjustment wouldprovide optimal correction of vision over the entire area of the lens,regardless of the focal distance of viewing angle. In practice, however,sensors provide an imperfect indication as to the desired focal distanceand angle of the eye at any given moment, and dynamic adjustment of thelens properties can therefore be uncertain. Furthermore, people withsevere limitations on their ability to accommodate for distance maybenefit from the use of a multifocal lens even when the focal length (orlengths) of the lens is electronically tuned.

Embodiments of the present invention that are described herein providenovel electrically-tunable lenses with properties that can be used,inter alia, to address the practical difficulties involved in dynamiccorrection of human vision. Some of these embodiments are useful inparticular in providing multifocal performance in such a lens.

The disclosed embodiments are based on optical devices that comprise anelectro-optical layer, such as a liquid crystal layer, having aneffective local index of refraction at any given location within theactive area of the layer that is determined by a voltage waveformapplied across the layer at that location. Conductive electrodes extendover both sides of the electro-optical layer, including, on at least oneof the sides, an array of excitation electrodes, which comprise parallelconductive stripes extending along respective, mutually-parallel axesacross the electro-optical layer. The electrodes on the opposing side ofthe electro-optical layer may comprise either a common electrode (inwhich case the device functions as a cylindrical lens) or an array ofparallel stripes oriented orthogonally to the stripes on the other side(so that the device functions in a manner that emulates a spherical oraspheric lens). Devices of this general type and details of theiroperation are described further in the above-mentioned PCT InternationalPublication WO 2014/049577. The principles of the disclosed embodiments,however, may alternatively be applied, mutatis mutandis, to other sortsof adaptive lens designs.

In some embodiments, each stripe of the excitation electrodes on atleast one side of the electro-optical layer is divided into two or moresegments, which extend over respective, mutually disjoint parts of theaxis of the stripe. Control circuitry applies respective control voltagewaveforms to the segments of the excitation electrodes so as to generatea specified phase modulation profile in the electro-optical layer.Specifically, the control circuitry can apply different control voltagewaveforms to the different segments of at least some of the excitationelectrodes, so that the lens functions as a multifocal lens, withdifferent zones having different optical powers. The control circuitrycan modify the control voltage waveforms applied to the electrodesegments in order to modify the phase modulation profile of one or moreof the different zones.

In some embodiments, the segmented stripes include one or more switchesinterconnecting the segments of the stripe. These switches are operableby the control circuitry to electrically join or separate the segmentsof the stripe. The control circuitry is thus able to dynamically changenot only the focal properties of the different zones of the lens, butalso their sizes and locations, by appropriately closing or opening theswitches.

Although some electro-optical materials, such as cholesteric liquidcrystals, operate on light regardless of polarization, mostcommonly-available liquid crystals and other electro-optical materialsare sensitive to polarization and may exert their refractive effect onlyon incident light of a certain polarization. This limitation of theelectro-optical material can limit the performance of adaptive spectaclelenses based on the material. Some of the embodiments of the presentinvention that are described herein overcome this limitation byinnovative use of polarization-rotating elements, and even turn thelimitation to advantage in enhancing performance of the spectacles.

In some of these embodiments, a polarization rotator intercepts incominglight that is directed toward an electrically-tunable lens and rotatesthe polarization of the intercepted light so as to ensure that the lightincident on the electro-optical layer has a component of polarizationthat will be refracted by the lens even if the intercepted light islinearly polarized in a direction orthogonal to the polarizationrefracted by the electro-optical material. The polarization rotatortypically comprises a quarter-wave plate or a birefringent plate, forexample. In one embodiment, a polarizer is interposed between thepolarization rotator and the electrically-tunable lens and is orientedso as to pass only the component of the light with the polarization thatwill be refracted by the lens. In an alternative embodiment, twoelectrically-tunable lenses, with electro-optical layers that areoriented to refract light with mutually-orthogonal polarizations, may bearranged in series so that incoming light of any polarization will befocused.

Some embodiments that are described herein provide adaptive spectaclescomprising electrically-tunable lenses, which are mounted in a spectacleframe along with a sensor, which senses the distance from the eye of aperson wearing the spectacles to an object viewed by the person. Controlcircuitry tunes the lenses according to the sensed distance, but it isnot always possible or desirable to determine the distanceunequivocally. Therefore, in some embodiments, the control circuitrytunes the lenses in the frame to have different, respective focal powers(also referred to as optical powers) that bracket the sensed distance.The term “bracket” is used in this context, in the present descriptionand in the claims, in the sense of focus bracketing, to mean that thefocal powers range around a certain target power value that is chosen onthe basis of the sensed distance. (The bracketing need not besymmetrical, and one of the focal powers can actually be the targetpower itself.) Such bracketing may be applied by the adaptive spectaclesnot only when the object distance is sensed automatically, but also toenhance the depth of field when the user sets the focal distancemanually.

Some of these embodiments make use of a pair of electrically-tunablelenses, as described above, with respective electro-optical layersoriented so that the first lens applies its focal power only to light ofa certain polarization, while the second lens applies its focal power,which is different from that of the first lens, only to light of theorthogonal polarization. In one embodiment, these two lenses arearranged to apply their focal powers to the light that is incidentrespectively on the left and right eyes of the person wearing thespectacles. In another embodiment, the two lenses are mounted one behindthe other in the spectacle frame so as to apply the respective focalpowers to the light that is incident on a single eye of the person. Ineither case, the person's eye or eyes will receive two images atdifferent focal lengths. Alternatively, both the right and leftelectrically-tunable lenses may apply their respective focal powersirrespective of polarization; for this purpose, the lenses may comprisean electro-optical material that is insensitive to polarization, or theymay comprise two polarization-sensitive lenses and/or lenses andpolarization rotators, as described above. In any of these cases, thebrain is capable of choosing and processing the image that is actuallyin focus on the object of interest.

System Description

FIG. 1 is a schematic, pictorial illustration of adaptive spectacles 20,in accordance with an embodiment of the invention. Spectacles 20comprise electrically-tunable lenses 22 and 24, mounted in a frame 25.The optical properties of the lenses, including focal length and opticalcenter (or equivalently, the optical axis) are controlled by controlcircuitry 26, powered by a battery 28 or other power source. Controlcircuitry 26 typically comprises an embedded microprocessor withhard-wired and/or programmable logic components and suitable interfacesfor carrying out the functions that are described herein. These andother elements of spectacles 20 are typically mounted on or in frame 25,or may alternatively be contained in a separate unit (not shown)connected by wire to frame 25.

Spectacles 20 comprise one or more sensors, which sense the distancefrom the eye of the person wearing the spectacles to an object 34 viewedby the person. Control circuitry 26 tunes lenses 22 and 24 according tothe sensor readings. In the pictured example, the sensors include a pairof eye trackers 30, which detect respective gaze directions 32 of theright and left eyes. Control circuitry 26 typically shifts therespective optical axes of lenses responsively to the sensed gazedirections. Furthermore, the control circuitry can use the distancebetween the pupils, as measured by eye trackers 30, to estimate theuser's focal distance (even without analyzing the actual gazedirection), and possibly to identify object 34.

A camera 36 captures an image of object 34, for use by control circuitry26 in identifying the object and setting the focal distance. Either eyetrackers 30 or camera 36 may be used in determining the focal distance,but both of these sensors can be used together to give a more reliableidentification of the object. Alternatively or additionally, camera 36may be replaced or supplemented by a rangefinder or other proximitysensor, which measures the distance to object 34.

In some embodiments, spectacles 20 also include at least one triggersensor 38, which activates the other components of spectacles 20. Forexample, trigger sensor 38 may comprise a timer that triggers controlcircuitry 26 and other elements periodically, or other sensorsindicating a possible change of the viewing distance, such as a headmovement sensor, or a user input sensor. In one mode of operation, whentrigger sensor 38 is actuated, camera 36 or other proximity sensorsdetect the distance to objects in the user's field of view. If allobjects in the field of view are at approximately the same distance,lenses 22 and 24 can be configured to focus the user's vision to thatdistance. If several objects are detected at different distances in theuser's field of view, eye trackers 30 are activated to determine thedistance at which the user is looking, for example by analyzing thedistance between the user's pupils.

Additionally or alternatively, control circuitry 26 may actuate thefunctions of spectacles 20 in response to user inputs. Various inputdevices (not shown in the figures) may be used for this purpose, forexample:

-   -   Buttons (push-buttons or touch buttons) on frame 25.    -   Eye-based gesture control systems, based on eye trackers 30 or        other sensors, which change the lens properties depending on eye        movements, winks and/or blinks.    -   Buttons placed on an external device, such as a wrist band,        which is connected to control circuitry 26 through a wired or        wireless communications link, such as a Bluetooth link.    -   Motion detectors on an external device such as a wrist band,        connected to the control circuitry 26 through a wired or        wireless communications link, which cause the control circuitry        to modify the lens properties according to specific movements,        such as wrist rotations or movements in specific directions.    -   Applications implemented on portable or wearable devices that        are connected to control circuitry 26 through a wired or        wireless communications link.    -   Voice control, in which control circuitry 26 modifies the lens        properties based on speech analysis or sound analysis to        identify predefined voice commands.

Further additionally or alternatively, control circuitry 26 may havepredefined operating modes, which are determined by user inputs and/orsensor inputs and can help in optimizing the focal distances of lenses22 and 24 under some conditions. Such operating modes may include, forexample:

-   -   Manual—The user manually selects a single distance (reading,        intermediate or far). Lenses 22 and 24 are adjusted accordingly,        and the automatic focusing system is disabled.    -   Office—Favors intermediate and close-range adjustment of lenses        22 and 24.    -   Standby—If no movement is detected for some time, shut down        sensors 30, 36 and lenses 22, 24 to save energy.    -   Driving—Favors far vision. For safety reasons, it is possible to        keep at least a portion of lenses 22 and 24 constantly at a far        vision setting and ignore shakes.    -   Reading—Favors close range, with switch to other ranges only in        special cases.    -   Normal—No context data. In this case, control circuitry relies        only on sensors 30, 36.

Precise detection of viewing distance by sensors 30 and 36 can bedifficult and uncertain, and erroneous setting of the focal powers oflenses 22 and 24 can be disturbing to the user. To alleviate thisproblem, lenses 22 and 24 may be set to different, respective focalpowers that bracket a certain target distance that is estimated based onthe sensors. This target distance is typically the estimated distance tothe object being viewed, such as object 34. The lens power disparitytakes advantage of the fact that binocular vision often requires onlyone eye to see a sharply-focused image in order for the view to seemfocused.

For example, if detectors 30 and 36 indicate that the target distance is1 meter, for which lenses 22 and 24 should be set to 1 diopter (relativeto the user's normal refractive corrections), and the user has atolerance for defocus of 0.2 diopters, then control circuitry 26 may setlenses 22 and 24 to respective powers of 0.8 and 1.2 diopters. Thisfocal bracketing gives the user the ability to see in focus over a widerrange of distances (corresponding to powers of 0.6 to 1.4 diopters), incase the detected distance was not accurate.

Lenses 22 and 24 can be operated with different optical powers at alltimes or only under certain circumstances in which the object distanceis uncertain. The difference between the focal powers of the left andright lenses (0.4 diopters in the example above) can be constant or varya function of several parameters, such as the level of confidence in theobject distance detected by sensors 30, 36; the probability distributionof the outputs of sensors 30, 36; lighting conditions; the detecteddistance itself; and the user's preferences.

In another embodiment, lens 22 (and/or lens 24) may comprise two or moreoptical elements that apply different, respective focal powers to theincoming light that is incident on one or both of the user's eyes. Theseoptical elements may be configured to refract light of differentpolarizations, for example by orienting the electro-optical layers inthe elements in orthogonal directions. This embodiment is describedfurther hereinbelow with reference to FIG. 2. Lenses 22 and 24 may beconfigured to operate on orthogonal polarizations in a similar manner.

As noted earlier, in some embodiments, control circuitry 26 uses thegaze directions indicated by eye trackers 30 in order to shift theoptical axes (i.e., to position the optical centers) of lenses 22 and 24dynamically to match the pupil locations, in addition to or instead ofadjusting the focal power. By shifting the optical axis with the pupil,the lens quality can be improved, particularly when the user is lookingthrough an area near the edge of the lens.

Erroneous shifts of the optical axis, however, can result in poor userexperience. In one embodiment, control circuitry 26 overcomes thisproblem by applying a predefined time lag when shifting the optical axesin response to changes in the sensed gaze direction. The optical centerof the lens thus moves gradually in response to eye movements, until itreaches the optimal position. Gradual movements of the lens center thatare slow enough not be noticeable by the user may produce a more naturalexperience for the user compared to abrupt lens shifts. The opticalcenters of lenses 22 and 24 can be moved either simultaneously orconsecutively, whether gradually or instantaneously in response to eyemovements.

Detailed Features of Electrically-Tunable Lenses

FIG. 2 is a schematic side view of electronically-tunable lens 22, inaccordance with an embodiment of the invention. Lens 24 is typically ofsimilar design.

In the pictured embodiment, lens 22 is a compound lens, which comprisesmultiple elements: A fixed lens 40, typically made from glass orplastic, provides a baseline optical power, which is modifieddynamically by two electrically-tunable lenses 42 and 44. (For thisreason, lens 22 itself can be considered an electrically-tunable lens.)Alternatively, lens 22 may comprise only a single electrically-tunableelement, and fixed lens 40 may not be needed in some applications. Insome embodiments, lens 22 also comprises a polarizing element 46, suchas a polarizer and/or polarization rotator, with functionality asdescribed hereinbelow.

Electrically-tunable lenses 42 and 44 adjust the optical power of lens22 depending on the focal distance to the object being viewed by theuser, while taking into account the considerations described in thepreceding section. Additionally or alternatively, an optical axis 48 oflenses 42 and 44 may be shifted in response to changes in gaze direction32, as was likewise described above. Lenses 42 and 44 may compriseelectrically-tunable cylindrical lenses, with orthogonal cylinder axes.Alternatively, lenses 42 and 44 may be configured, as shown in FIGS.3A-3D, to generate two-dimensional phase modulation profiles and thusemulate spherical or aspheric lenses (or their Fresnel equivalents).Both of these sorts of lens configurations, as well as waveforms fordriving the lenses, are described in detail in the above-mentioned WO2014/049577.

As noted earlier, in some embodiments in which lenses 42 and 44 compriserespective polarization-dependent electro-optical layers, the two lensesare oriented so as to refract mutually-orthogonal polarizations: One ofthese lenses, for example, lens 42, operates on light polarized in theX-direction (pointing into the page in the view shown in FIG. 2), anddoes not influence light polarized in the Y-direction (pointing upwardin this view). Lens 44 operates on light polarized in the Y-direction,possibly with a different focal length from lens 42, and does notinfluence light polarized in the X-direction. Unpolarized light passingthrough lenses 42 and 44 will thus be focused at both distances, withroughly half the light focused according to the focal length of lens 42,while the other half is focused according to the focal length of lens44.

This solution may not work for objects that emit polarized light, suchas light emitted from electronic displays. In this case, if the light ispolarized in the same direction as one of lenses 42 and 44, then all ofthe light will be focused according to the focal length of that lens.

To avoid this sort of polarization-dependence, in some embodimentspolarizing element 46 comprises a polarization rotator, which interceptsthe incoming light and rotates its polarization so as to ensure that thelight incident on the electro-optical layers of lenses 42 and 44 has acomponent at each of the respective polarizations, regardless of theinitial polarization of the intercepted light. For example, in oneembodiment, polarizing element 46 comprises a quarter-wave plate,typically with a wide optical bandwidth. The axes of the quarter-waveplate are oriented at a 45° angle with respect to the polarization axesof lenses 42 and 44. The polarization of any linearly-polarized lightpassing through the quarter-wave plate will then be rotated so that theenergy is divided equally between the orthogonal polarization directionsof the lenses and will be focused at the focal lengths of both of lenses42 and 44 just as in the case of unpolarized light. Lenses 22 and 24 inspectacles 20 (FIG. 1) may contain respective quarter-wave plates thatrotate the polarization either in the same direction or in oppositedirections.

In an alternative embodiment, polarizing element 46 comprises atransparent birefringent plate, creating a wavelength-dependentpolarization rotator. A layer with birefringence Δn(λ), as a function ofthe wavelength λ, and thickness d creates a wavelength-dependentpolarization rotator, with relative phase retardation between the axesgiven by Δφ(λ)=2π/λ dΔn (λ). The birefringent plate in lens 22 isoriented so as to rotate the polarization of light that enters the platewith polarization along either the X- or Y-axis (assuming that these arethe polarization axes of lenses 42 and 44). The amount of rotationdepends on the wavelength λ and the thickness d. As long as thebirefringent plate is sufficiently thick, the intensity of the lightexiting the plate, when averaged over any but a very narrow range ofwavelengths, will be divided equally between the X- and Y-polarizations.This arrangement ensures that half of the light will be focused by lens42 and the other half by lens 44.

In some embodiments, polarizing element 46 also comprises a polarizer,which is interposed between the polarization rotator and lens 42 and isoriented so as to pass the polarization component that is focused bylens 42. (In this case, lens 44 may be omitted, or else lenses 42 and 44may be cylindrical lenses, with the same axis of polarization.) Lens 22will then operate on light of any polarization, regardless of itsorientation. As in the preceding embodiments, the polarization rotator(such as a quarter-wave plate or birefringent plate) is oriented withits axis at a 45° angle relative to the polarization axis of lens 42.The polarizer is oriented so that its polarization axis is parallel tothat of lens 42. This arrangement ensures that for anylinearly-polarized light (and unpolarized light as well), half of theintensity will be passed through to lens 42, polarized parallel to thepolarization axis of the lens, so that lens 42 will focus the light asdesired.

FIGS. 3A-3D schematically show details of electronically-tunable lens 42in accordance with an embodiment of the present invention. FIG. 3A is apictorial illustration of lens 42, while FIGS. 3B and 3C are side viewsshowing transparent substrates 52 and 54 on opposing sides of anelectro-optical layer 50 in lens 42. FIG. 3D is a side view of device42, showing a superposition of excitation electrodes 56 and 60 that arelocated on substrates 52 and 54 on the opposing sides of lens 42. Lens44 may be of similar design.

Electro-optical layer 50 typically comprises a liquid-crystal layer, asdescribed in the above-mentioned PCT International Publication WO2014/049577. As explained above, layer 50 typically refracts light, inresponse to the voltage waveforms applied by electrodes 56 and 60, inonly one direction of polarization, while the other polarization passesthrough lens 42 without refraction. Alternatively, layer 50 may comprisea cholesteric liquid crystal or other electro-optical material that ispolarization-independent.

Electrodes 56 and 60 on substrates 52 and 54, respectively, compriseparallel stripes of transparent conductive material extending over theactive area of layer 50 in mutually-orthogonal directions. Althoughelectrodes 56 and 60 are of uniform shape and spacing in the figures,the stripes may alternatively have varying sizes and/or pitch. As shownin FIG. 3D, the superposition of electrodes 56 and 60 creates an arrayof pixels 64, defined by the areas of overlap of the vertical stripes ofelectrodes 56 with the horizontal stripes of electrodes 60.

Control circuits 58 and 62, under the control of control circuitry 26 oranother controller, apply control voltages to excitation electrodes 56and 60, respectively. As described in the above-mentioned WO2014/049577, the control circuits in lens 42 are able to modify thecontrol voltages applied to each of a set of the excitation electrodes(which may include all of the electrodes) simultaneously andindependently. Control circuits 58 and 62 together can modify thevoltages applied to sets of the excitation electrodes on both of thesides of layer 50, thereby modifying the phase modulation profile of thelayer in two dimensions.

The control voltages applied to excitation electrodes 56 and 60 tune thefocal properties of lens 42, as determined by the phase modulationprofile. Control circuits 58 and 62 can modify the control voltages soas to change the focal length and/or to shift the optical axis of thelens. The voltage patterns applied by circuits 58 and 62 acrosselectrodes 56 and 60 may be chosen so as to give a phase modulationprofile that is circularly symmetrical, and may thus emulate a sphericalor aspheric lens. Alternatively, different voltage patterns may beapplied so that lens 42 functions, for example, as an astigmatic lens,with a stronger cylindrical component along one axis or the other.

Partitioned Dynamic Lenses

In some cases it may be desirable to partition the area of anelectronically-tunable lens, such as lenses 22 and 24, into twoindependent lenses. For example, spectacles 20 may be configured so thatin some scenarios, the lenses are partitioned, with part of the lensesset constantly for the user's vision correction to infinity, and theother part changing dynamically. The embodiments described below supportoptional spatial partitioning of the area of an electronically-tunablelens. The lens in these embodiments either can be operated as a singlelens spanning over all (or at least part) of the active area, or theactive area can be partitioned into two or more regions, each regionimplementing different lens characteristics (such as focal length and/oroptical axis). The lenses can be made to switch dynamically betweenthese modes.

FIG. 4 is a schematic frontal view of electrodes formed on a substrate70 for use in a partitioned, electronically-tunable lens, in accordancewith an embodiment of the invention. Substrate 70 and the electrodesformed thereon may be used in lens 42, for example, to apply voltagewaveforms to layer 50 (FIGS. 3A-3D) in place of substrate 52 andelectrodes 56. Electrodes 60 on substrate 54 may remain as shown in FIG.3C, or they may alternatively be partitioned in a manner similar to thatshown in FIG. 4. Further alternatively, to produce a partitionedcylindrical lens, electrodes 60 may be replaced on substrate 54 by asingle, common electrode (not shown in the figures).

The electrodes on substrate 70 comprise an array of parallel conductivestripes extending along respective, mutually-parallel axes across theactive area of the electro-optical layer. Each stripe is divided intotwo segments 76 and 78, extending over respective, mutually disjointparts of the axis of the stripe. (In alternative schemes, such as thedynamic scheme illustrated in FIG. 5, each stripe may be divided intothree or more segments.) Typically, although not necessarily, segments76 are connected to and controlled from conductors at the upper edge ofsubstrate 70 in the view shown in FIG. 4, while segments 78 areconnected to and controlled from conductors at the lower edge.

Segments 76 together extend across and cover an area 72 of the lens,while segments 78 extend across and cover a different area 74. Controlcircuitry 26 is able to apply different control voltage waveforms to thesegments in area 72 from those applied to the corresponding segments inarea 74, and thus causes the lens to function as a multifocal lens, withdifferent focal zones corresponding to areas 72 and 74. Typically, thefocal zones have different, respective focal lengths. When desired,however, the same waveforms may be applied to each segment 76 as to itscounterpart segment 78 in each stripe, so that both areas 72 and 74 havethe same focal characteristics.

FIG. 5 is a schematic electrical diagram showing electrode segments 82and switches 84 formed on a substrate 80 in an electronically-tunablelens, in accordance with an alternative embodiment of the invention.Each stripe may comprise as few as two segments 82, as in the precedingembodiment. In the embodiment shown in FIG. 5, however, each stripe isdivided into n segments 82, labeled R1, R2, . . . , Rn, which areinterconnected in series by switches 84, labeled G1, G2, . . . , Gn−1,such as suitable thin-film transistors. Control lines 86 are connectedto actuate corresponding rows of switches 84 across all of the stripes,with a single control line connected to each switch Gi over all of thestripes. By actuating the appropriate control lines, control circuitry26 is thus able to electrically join or separate each segment to or fromits neighbors in all of the stripes simultaneously.

In order to achieve good optical quality, the gaps between segments 82are typically much smaller than the lengths of the segments themselves.The segments can all be of similar lengths, as in the example shown inFIG. 5, or different segments can have different lengths, both withineach stripe and between different stripes.

Control circuitry 26 is typically connected to apply the control voltagewaveforms to one or both ends of each of the conductive stripes, forexample, to segment R1 and possibly segment Rn in each stripe. To applydifferent, respective control voltage waveforms to different segments,the control circuitry can actuate the appropriate switches 84 and modifythe control voltage waveforms applied to the respective ends of theconductive stripes.

For example, in order to partition lens 80 along the line of switchesGi, control circuitry 26 sets all of control lines 86 for k≠i to turn on(close) the corresponding switches Gk, so that the neighboring segments82 are electrically joined together. At the same time, control line i isset to turn off (open) switches Gi, thus separating the segments Ri andRi+1 along the partitioning line. Control circuitry 26 applies voltagewaveforms to segments R1 that are chosen to implement a first set offocal characteristics. These waveforms pass through switches 84 and thuspropagate down through segments 82 in each stripe until they reach theopen switches Gi. In a similar fashion, control circuitry 26 appliesother waveforms to segments Rn, chosen so as to implement differentfocal characteristics, and these waveforms pass through switches 84 andsegments 82 up to the same separating line at switches Gi.

In another embodiment, lens 80 is used to implement a partitioneddynamic lens in which each of two or more zones, as defined by a row ofsegments or a group of such rows, can be set to implement differentfocal characteristics (focal length and/or optical axis), with controlcircuitry connected to segment R1. Zones 1, . . . , n, corresponding tosegments R1, . . . , Rn, can be made to implement focal characteristicsF1, . . . , Fn by applying the following steps:

1) Set all switches, Gk, k=1 . . . n−1 to ‘on’.

2) Apply voltages to the electrodes to implement focal characteristicsFn.

3) Repeat for j=n−1 to 1:

-   -   a) Set switch Gj to ‘off’.    -   b) Apply voltages to the electrodes to implement lens Fj.        Using this method, switches 84 are turned off (opened) one row        at a time. The voltages of the electrode segments in section Rj        are updated during the interval between the opening of switch j        and the opening of switch j−1. It is desirable that the duration        of this interval be kept to a minimum, but it should be long        enough to ensure that the voltages on segments Rj reach their        final values and are updated correctly.

The voltage applied to each electrode segment Rj changes over time: Whensegments Rj+1 . . . Rn are updated, this voltage may be different fromthe voltage required to implement the correct focal characteristics Fjfor zone j of the lens. Since liquid crystal is affected by thetime-average voltage applied to it, these voltage changes can add noiseto the modulation function of zone j. This noise can be reduced bymodifying the voltage applied to the electrodes when each segment Rj isupdated so as to compensate for the voltages that were applied whensegments Rj+1 . . . Rn were updated, such that the time-average voltageon segment Rj has the desired value.

To enhance the efficiency of this scheme, if adjacent segments 82require similar driving voltages (and thus implement similar lenses),they can be updated simultaneously by closing switches 84 bridgingbetween these segments.

Additionally or alternatively, control circuitry 26 can be connectedboth to segment R1 and to segment Rn in each stripe, and can use apropagation sequence similar to that described above simultaneously fromR1 downward and from Rn upward. In this manner, the voltages of allsections of the lens can be updated in a shorter time.

It will be appreciated that the embodiments described above are cited byway of example, and that the present invention is not limited to whathas been particularly shown and described hereinabove. Rather, the scopeof the present invention includes both combinations and subcombinationsof the various features described hereinabove, as well as variations andmodifications thereof which would occur to persons skilled in the artupon reading the foregoing description and which are not disclosed inthe prior art.

1. Optical apparatus, comprising: an electrically-tunable lens, comprising: an electro-optical layer, having, for a given polarization of light incident on the layer, an effective local index of refraction at any given location within an active area of the electro-optical layer that is determined by a voltage waveform applied across the electro-optical layer at the location; conductive electrodes extending over opposing first and second sides of the electro-optical layer, the electrodes comprising an array of excitation electrodes extending across the first side of the electro-optical layer; control circuitry, which is coupled to apply respective control voltage waveforms to the excitation electrodes so as to generate a specified phase modulation profile in the electro-optical layer; and a polarization rotator, positioned and configured to intercept incoming light that is directed toward the lens and to rotate a polarization of the intercepted light so as to ensure that the light incident on the electro-optical layer has a component of the given polarization regardless of an initial linear polarization of the intercepted light.
 2. The apparatus according to claim 1, wherein the polarization rotator comprises a quarter-wave plate.
 3. The apparatus according to claim 1, wherein the polarization rotator comprises a birefringent plate.
 4. The apparatus according to claim 1, and comprising a polarizer, which is interposed between the polarization rotator and the electrically-tunable lens and is oriented so as to pass the component of the given polarization.
 5. A method for producing optical apparatus, the method comprising: providing an electrically-tunable lens, comprising: an electro-optical layer, having, for a given polarization of light incident on the layer, an effective local index of refraction at any given location within an active area of the electro-optical layer that is determined by a voltage waveform applied across the electro-optical layer at the location; conductive electrodes extending over opposing first and second sides of the electro-optical layer, the electrodes comprising an array of excitation electrodes extending across the first side of the electro-optical layer; control circuitry, which is coupled to apply respective control voltage waveforms to the excitation electrodes so as to generate a specified phase modulation profile in the electro-optical layer; and positioning a polarization rotator to intercept incoming light that is directed toward the lens and to rotate a polarization of the intercepted light so as to ensure that the light incident on the electro-optical layer has a component of the given polarization regardless of an initial polarization of the intercepted light.
 6. The method according to claim 5, wherein the polarization rotator comprises a quarter-wave plate.
 7. The method according to claim 5, wherein the polarization rotator comprises a birefringent plate.
 8. The method according to claim 5, and comprising interposing a polarizer between the polarization rotator and the electrically-tunable lens and orienting the polarizer so as to pass the component of the given polarization. 